1. Field of the Invention
The present invention relates to a method of manufacturing an epoxy resin composition for semiconductor encapsulating, an epoxy resin composition for semiconductor encapsulating manufactured by the method, and a semiconductor device encapsulated with the epoxy resin composition for semiconductor encapsulating.
2. Description of the Related Art
In general, a resin composition for semiconductor encapsulating is comprised of an epoxy resin having excellent electrical properties, heat resistance and mass productivity, a curing agent for the epoxy resin, a catalyst, a release agent, a flame retardant, an additive such as a coloring agent, and a filler which occupies 70 to 95 wt % in terms of a composition ratio. Furthermore, its manufacturing method comprises the steps of blending and mixing predetermined amounts of components constituting the resin composition, kneading the mixture by the use of a mixing mill, a uniaxial kneader, a combination of the uniaxial kneader and the mixing mill, or a biaxial kneader, rolling the kneaded material into a sheet form, cooling the sheet, pulverizing the cooled sheet, and then, if necessary, forming the pulverized material into cylindrical tablets. In the kneading step of these steps, the biaxial kneader which is excellent in productivity has often been used as the kneader.
However, the biaxial kneader has a hermetically sealed inside structure, and hence, in a case where a gas is volatilized from the kneaded material, the volatile gas is discharged out of the kneader through a discharge orifice of the kneader. When the volatile gas contacts with a cooled member for the discharge orifice of the biaxial kneader, the volatile gas comes to be cooled and liquefied, and the resultant liquid then adheres to the member for the discharge orifice. Particularly, when the liquid adheres to a portion close to the discharge orifice of the kneader, there is a fear that the liquid mingles with the kneaded material or drops onto sheet forming rolls for cooling the kneaded material.
In such a case where the liquid mingles with the kneaded material, there is a fear that voids (pores) are generated during the molding of semiconductor packages. Furthermore, when the liquid adheres to the sheet forming rolls, there is also a fear that a trouble occurs during the operation of the kneader.
As means for solving the above problem, there has been disclosed a biaxial kneader characterized by the shape of a vent port to efficiently discharge a volatile gas (see Japanese Patent Application Laid-open No. 7-314440). Furthermore, a method for carrying out the kneading operation while maintaining the pressure in the kneader at a reduced pressure of 250 mmHg or lower has also been proposed (see Japanese Patent No. 3009027 and Japanese Patent No. 3320354).
In these methods, it is necessary to seal a kneading section of the kneader with a kneaded material to create the conditions of the reduced pressure. This is apt to cause the movement of the kneaded material toward a suction port, clogging of a discharge orifice and the like, which makes continuous production difficult.
Therefore, at the production site of a conventional epoxy resin composition for semiconductor encapsulating, prescribed maintenance such as removal of the resin composition adhering to a part of the kneader has been carried out in a case where the kneader is continuously operated.
In the meantime, in recent years, semiconductor packages are becoming increasingly thinner so that a material for semiconductor encapsulating is also decreasing in thickness in the package. The presence of the voids makes it difficult to secure desired moisture resistance reliability and electric insulation properties. For this reason, there has been a strong demand for a means for removing volatile components to prevent the generation of the voids.
Therefore, in order to solve such conventional problems, it is an object of the present invention to provide a method of manufacturing an epoxy resin composition for semiconductor encapsulating, by which a volatile gas can be efficiently discharged even under a condition of continuous kneading operation.